Investigating the effect of nanosilica on the compressive strength of hard concrete by considering Atomic Force Microscopy (AFM) examinations

This study investigated the compressive strength of hardened concrete and the formation of Calcium Silicate Hydrate (C-S-H) with the addition of nanosilica (SiO2). Compressive strength testing was performed using ASTM C496 to determine stress-strain curves and compressive strength of the materials. The hydration process and formation of C-S-H and Calcium Hydroxide (CH) was examined using Atomic Force Microscopy (AFM) and Fourier Transform Infrared Spectroscopy (FTIR). Results indicate an increase in compressive strength using 1, 3 and 5% of nanosilica to concrete replacement by volume in comparison to the control mix (without nanosilica). The optimum concrete replacement to yield maximum strength was of the 5% nanosilica content. Comparing the 56 day results for the 3 and 5% of nanosilica replacement samples, notice the same percentage of C-S-H formation of 83 and 85%, respectively